Generated set properties share the same instance

[jeroenvs]

Using the BeanBuilder.fill() method causes set and other collection based properties to reuse the same mutable collection instance. When the collection is decorated it will cause followup tests to fail.

Please use the immutable collections as default:

        registerValue(List.class, List::of);
        registerValue(Set.class, Set::of);
        registerValue(Collection.class, List::of);
        registerValue(Map.class, Map.of);